The application of experimental design to investigate the solvent matrix effects observed during the Determination of Rhodium (Rh) in organic media by Graphite Furnace Atomic Absorption Spectrometry (GFAAS)

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The application of experimental design to investigate the solvent matrix effects observed during the Determination of Rhodium (Rh) in organic media by Graphite Furnace Atomic Absorption Spectrometry (GFAAS)

Abstract:

In an industrial application a GFAAS method for monitoring the Rh concentration in
process streams is being used. Matrix effects are known to exist with the application of
this technique; in fact, it was observed that different solvents lead to different results.
Therefore, standard additions have to be employed for quantitative determinations,
resulting in high costs and long analysis times. In an attempt to understand these
interfering effects, fractional factorial designs were proposed to determine whether any
GFAAS parameter was responsible for, or related to, the matrix effects. Seven GFAAS
parameters were investigated: final temperature, ramp time and hold time of the
transitions step (from the dry step); final temperature, ramp time and hold time of the
ashing/pyrolysis step; ramp time of the atomisation step. The results showed that the
matrix effects were not related to any specific parameter. A complete factorial design
was implemented to demonstrate the fundamental role of the atomisation temperature.
SEM analysis showed that the surface of the graphite tubes might be affected in different
ways by different solvents. A Principal Component Analysis demonstrated that the
matrix effects may be related to the viscosity and melting point of the solvents and may
be independent of their molar mass. To identify the origins of these effects, an
investigation on the link between the tube surface-sample matrix interactions and the
physical properties of the matrices is recommended. Since GFAAS parameters cannot
compensate for the matrix effects, standard additions remain the preferred mode of
operation as it accounts for the effects in-situ.